1. Field of the Invention
The present invention relates to ionic compounds in which the anionic charge is delocalized, and their uses.
2. Description of the Background
It is known and it is particularly interesting to introduce ionic groups in molecules or organic polymers having various functions. Coulombic stresses correspond, indeed, to the stronger interactions which are available at the molecular level, and the ionic groups modify in an utmost manner the molecules to which they are bonded. Coloring matters which are made soluble in water by means of sulfonate or carboxylate functions may be mentioned.
However, the groups of this types, --CO.sub.2.sup.- 1/mM.sup.m+ or --SO.sub.3.sup.- 1/mM.sup.m+, are not dissociated, and they do not induce solubility in solvents other than water or certain highly polar protic solvents such as light alcohols, which considerably restrict the scope of their utilization.
On the other hand, salts of the compounds [R.sub.F SO.sub.2 --N--SO.sub.2 R.sub.F ].sup.- 1/mM.sup.m+ in which R.sub.F is a perfluorinated group and M.sup.m+ is a cation of valence m+ are known, which are soluble and are dissociated in organic aprotic media or solvating polymers. It is however considered that the existence of two perfluoroalkylsulfonyl groups (in particular the existence of fluorine atoms on the .alpha. atom of carbon of each sulfonyl group) which exert an important attracting power on the electrons of the ionic charge, is a necessary condition to obtaining properties of solubility and dissociation. For example, the pK.sub.a of the acid H[CF.sub.3 SO.sub.2 --N--SO.sub.2 CF.sub.3 ] is only 1.95, which compares to that of the non-fluorinated acid CH.sub.3 SO.sub.3 H (pK.sub.a =0.3) and is clearly inferior to that of perfluorinated acid CF.sub.3 SO.sub.3 H (pK.sub.a &lt;-9) because of the basic character of the central nitrogen atom with respect to the oxygen atom of sulfonic acids.